This invention relates to an apparatus and method for enlarging a pilot hole such as the inverted arcuate type. More specifically, this invention relates to an apparatus and method for enlarging a pilot hole by means of a hole opener apparatus which may be guided through the pilot hole by a pull tubing or cable to which the hole opener is attached. In one embodiment of the invention, the lead end of the hole opener is rotatably mounted relative to the pull tubing or cable as the hole opener is guide through the pilot hole during enlargement thereof.
Drilling techniques for producing bore holes of the type to which both ends of the bore hole are freely accessible to drilling equipment, to installation of casing, and other procedures usually employed in this art are well known. Reference may be had to the following patents and publications which illustrate the state of the prior art: Zublin, "Horizontal Drilling", Oil Weekly Oct. 1, 1945, p. 35 etc. U.S. Pat. Nos. 3,720,272, 3,667,556, 2,646,253, 2,646,254, 2,656,294, U.S.B.M. Contract Report 1 to 111355 "Dyna Drill" Handbook issued by the Dyna Drill Division of Smith International Corp., 2nd Edition, World of SII, Sept. 1972, Pipe Line and Gas Journal" under "A River Crossing Proves Directional Boring Device", Jan. 4, 1973, and "Directional Drilling Adopted For Pipe Line River Crossing." Pipe Line Industries, Sept. 1974. U.S. Pat. Nos. 3,878,903 and 3,894,402.